Various driving force controlling (so-called traction controlling) apparatuses for a vehicle which control an ignition time or an air/fuel ratio to prevent a slip of a wheel are conventional. For example, in Japanese Patent Laid-Open Application No. 1-170726, a technique is disclosed wherein a driving force is gradually returned to a standard condition when a front wheel sensor or a rear wheel sensor for detecting a front wheel velocity or a rear wheel velocity, which is necessary to detect a slip level of the vehicle, fails.
Since data of the front wheel velocity and the rear wheel velocity have some dispersion, the average values are calculated. The average values are then used for detection of a slip level described above.
Such a failure of a front wheel sensor or a rear wheel sensor as described above can be detected by a microcomputer which executes a predetermined failure determination process. Some time lag can exist after the sensor has actually failed until the microcomputer detects the failure.
Accordingly, even if a predetermined condition (driving force control starting condition) is satisfied and control is changed over from standard control to driving force control during the time lag mentioned above, there is the possibility that a signal (ignition time) for driving force control may be calculated using wheel velocity data different from an actual wheel velocity, which is not preferable. When the driven wheel velocity decreases and the driven wheel velocity is 0 or so, a slip is detected and output power control is performed, whereafter the failure is detected, and consequently, the control will enter a failure mode in the output power control.